1. Field of the Invention
The present invention concerns an wear resistant powder sintered alloy having corrosion resistant property, particularly, to halogen gases such as fluorine gas, SOx gas, NOx gas, etc. and suitable to application for molding apparatus of plastics, rubbers or ceramics that release these gases.
2. Description of the Prior Art
Since injection or extrusion molding of plastic materials are conducted at a rather high temperature conditions, heat decomposition can not be avoided for a portion the starting material used therefor and evolution of corrosive gases has been considered more or less inevitable. Particularly, in the case of blending halogen-containing compounds with an aim of providing flame retardancy, a great amount of halogen-containing gases are released. Then, the inside of the cylinder is always exposed to a corrosive circumstance and, accordingly, corrosion resistance at high level is required for the cylinder. Besides, since a considerably high pressure is loaded upon molding and the strength of inorganic fillers often blended in order to improve the strength is extremely high, high wear resistance is also required for the cylinder.
Particularly, materials of injection and extrusion molding machines for fluoro resins are required to have extremely high corrosion resistance capable of withstanding highly corrosive gases. Further, since corrosive gases are evolved also in the case of cutting and scraping those molding products made of fluoro resin and fluoro rubber, countermeasures for the corrosion and the wear are important.
In injection molding or extrusion molding of plastic materials such as synthetic plastics, for example, PES (polyether sulfone) or PPS (polyphenylene sulfide) resins or rubbers, heated plastic materials are charged in a cylinder and molded by applying pressure from a plunger. Since the molding operation is conducted at a rather high temperature condition and since SO.sub.2 gases are evolved from sulfone groups in the plastic materials such as heated resins, it is necessary to use those materials excellent in corrosion resistance as well as wear resistance.
Furthermore, in the injection molding or extrusion molding of plastics such as ABS resins, since NOx is released from CN groups or corrosive gases such as halogen gases are evolved from heated plastic materials such as resins, those materials excellent in the corrosion resistance as well as the wear resistance have to be used.
Self-melting abrasion resistant Ni-based alloys and Co-based alloys have usually been used as the cylinder material of this type and they are utilized by lining to the inside of the cylinder by a centrifugal casting method.
In different form of application uses, Ni-MO-Cr alloys of excellent corrosion resistance are also used.
However, although the former self-fluxing wear resistant alloys are excellent in the wear resistance, corrosion resistance of them to corrosive gases is not sufficient and, particularly, the corrosion resistance to highly corrosive fluorine gas among halogen gases, SO.sub.2 gas and NOx gas is extremely poor. On the other hand, although the latter Ni-Mo-Cr alloys are satisfactory in the corrosion resistance, they are poor in the wear resistance as the cylinder or screw. As described above, none of the alloys mentioned above can be said to satisfy both of the corrosion resistance and the wear resistance.
In order to overcome these problems, the present inventors have previously proposed highly corrosion resistant and abrasion resistant alloys as described in Japanese Patent Application Laid-Open Nos. Sho 61-143547 and 62-142705. These alloy have a composition comprising 0.5-3.0% of Si, 0.5-3.0% of B, 10-40% of Cr, 0.5-3.0% of Cu and the substantial balance of Ni or Co.